Some embodiments according to the invention are related to a method of dicing a semiconductor wafer. Some embodiments according to the invention are related to a wafer as an intermediate product during the method of dicing the wafer. Some embodiments according to the invention are related to a semiconductor device obtained from the method of dicing a wafer.
The semiconductor integrated circuits (or devices, or chips) that are manufactured on wafers typically need to be kept apart from each other by a given distance. This distance is called dicing street, scribe-line, kerf, dicing channel, etc.
This distance is needed so that the singulation process that is normally based on a disruptive mechanical sawing process can be performed without damaging the circuits. The sawing process is normally conducted by means of a rotating diamond circular blade. In recent times, a prescribing process assisted by an ablation laser is utilized. The kerf, which surrounds each chip on its four sides has a width which varies from technology to technology. By making use of conventional blade dicing and taking into account the stringent manufacturing quality and reliability requirements of today's mass production standards (e.g., Zero Defect Policies), the narrowest available kerf released in production appears to be approximately 62 μm wide.
The area required for the kerf is typically destroyed during the dicing process. For this reason, temporary structures may often be found in the kerf area. For example, within the space of the kerf, a number of structures necessary to control the manufacturing operations may be placed. Such structures comprise the typical process control monitor electrical test structures (PCM), the photolithographic alignment structures, the wafer level reliability test circuits, the film thickness and critical dimension (CD) measurement structures, etc. When the mechanical rotating blade-assisted dicing operation is performed, the wafer state of the kerf is wasted and mentioned test structures are destroyed. The width of the kerf is essentially determined by the following factors: The width of the dicing blade, the width of the test and measurement structures plus margins for quality and reliability concerns.
When making use of mechanical rotating blade-assisted dicing, the following observations can typically be made:
The smaller the area of the chip, the higher the percentage of wafer material wasted in the kerf.
The edges of the singulated die are particularly rough and there is a high risk of chipping of the upper films of the chip.
Micro-cracks can be easily generated which propagate within the integrated circuit (which can pose reliability constraints); consequently, the integrated circuit has to be protected from crack issues by means of “crack stop” structures, which, in turn, increase the chip area.
Generation of wafer dust (generally silicon) that can lead to discoloration/corrosion of the input/output circuit pads (generally made of aluminum).
The utilization of water, intended to cool down the blade and wash out the dirt, can lead to corrosion of the aluminum of the pad.
The dicing has to be performed along perpendicular and/or rectangular kerf lines.
During the last few years, a new sawing/dicing technology has emerged in the industry, known as Stealth Dicing, which relies on a laser beam to perform the singulation of the dies. The main characteristic of such a Stealth Dicing technology is that the laser beam is focused at a selectable depth within the bulk of the wafer. The energy carried by the laser beam is therefore capable of locally modifying the morphology of the crystalline wafer (e.g., silicon, GaAa, etc.) from mono-crystalline to poly-crystalline. As a result, a precisely localized line of mechanical stress is introduced within the bulk of the wafer at the selected depth. Once the wafer has been processed through the Stealth Dicing tool, it is still not yet singulated. In order to separate each die from its neighbor, it is necessary to apply a controlled mechanical expansion of the wafer; such an operation is performed in a separate module of the Stealth Dicing machine called expander.